Windows Template Library, or WTL, is a set of classes that extend ATL to support more complex user interfaces for either applications or various UI components, while maintaining the big advantage of ATL – small and fast code. WTL classes were designed to be the best and the easiest way to implement rich Win32 based UI for ATL based applications, servers, components, and controls.
WTL provides support for implementing many user interface elements, from frame and popup windows, to MDI, standard and common controls, common dialogs, property sheets and pages, GDI objects, UI updating, scrollable windows, splitter windows, command bars, etc. The WTL classes are mostly templated and use minimal instance data and inline functions. They were not designed as a framework, so they do not force a particular application model, and can accommodate any. The classes do not use hooks or thread local storage, so they have no restrictions that those techniques impose. They also have no inter-dependencies and can be freely mixed with straight SDK code. In summary, WTL delivers very small and efficient code, very close in size and speed to SDK programs, while presenting a more logical, object oriented model to a programmer.